Note: Descriptions are shown in the official language in which they were submitted.
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PULVERtZER APPARATUS WITH HORLZONTAL AXIS PIVOT SCRAPER
BACKGROUND OF THE INVENTION
The invention relates to pulverizers of the type that are used in pulverized
coal fired
steam generating systems. More partiarlariy, the invention relates to
apparatus that
serapes accumulated substances from the underbowl of a bowl mill.
Pulverized coal firtng is fawned over other methods of burning coal because
pulverized
coal bums like gas and, therefore, fires are easily lighted and controlled.
Pulvertzers, also referred to as mills, are used to grind or comminute the
fuel. The
present invention has primary application to bowl pulverizers or mills.
Although the
present invention will be described with respect a bowl type ring roll
pulverizes. Those
skilled in the art will recognize that the invention may be used in other bowl
type milts
as well.
In the operation of a pulverizes coal enters the center of the pulverizes and
through a
center feed pipe. The coal is pulled onto a rotating bowl which has a
replaceable wear
surtace. Centrifugal force causes the coal to move outward from the center and
under
three journal assemblies, where it is cnrshed by large rolls. The partially
pulverized
coal passes over the rim of the bowl and is it entrained by a rising hot air
stream.
Pyrites and tramp iron that enter the mill with the coal follow the same path
as the coal
until they pass over the rim of the bowl. Because these materials are more
dense than
coat, they are not carried any further upward by the air stream and fall into
an
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underbowl. In addition to pyrites and tramp iron there may be other heavy
foreign
materials that may be found in the coal that will also fall into the
underbowl.
These materials are both very abrasive and erosive. Removal of these materials
from
the underbowl requires the use of a saaper to mechanically push the materials
toward
an olrtlet chute. The abrasion and errosion caused by these materials is
prejudiaal to
the service life of the scraper apparatus.
The host<le environment in which the scraper mechanism must operate witl be
more
1 o apparent by considering both the nature of the materials that pass through
the
pulverizer as well as the quality of material that flows through the
pulverizes A typical
pulverizes has a capadty of up to 200,000 pounds of coal per hour.
Prior art scrapers have induded a generally planar scraping element carried on
a
vertical axis. Cenfiifugal forces urge the scraping element to a generally
radial
positron. A central body caries the vertical axes of the soaping elements. As
the
central body rotates the soaping elements are urged by centrifugal forces to
generally
radial positions about the underbowl. If a large object falls into the
underbowl the
scraping element can move from the radial position upon impact with the large
object
and then return to the radial position after passing the large object.
It is believed that the vertical axis of the prior art scraper inherently
positions a part of
the bearing surface in close prox>mity to severely hostile abrasive and
erosive
environment . More particulariy, the lower extremity of the vertical axis
inherently must
be very dose to a hostile environment that it is prejudicial to the bearing.
Another concern with the prior art scraper assembly is that it requires
installation of a
complete assembly to repair worn parts.
In some cases wear of the vertical axis and journal bearing cooperating with
the axis
may allow the generally planar scraper element to droop so that the radial
extremity of
scraper element contacts the surtace of the bowl and causes wear. Such
construdyons
have been satisfactory for many installations. However, in some installations
the
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materials found within a particular coat may be more abrasive and more erosive
than
in other coats from other parts of the world.
Another concern is that heavy assemblies are more difficult to install.
SUMMARY O>~ THE INVENTION
It is an object of the present invention to provide a scraper apparatus that
will have a
longer service life,
It is another object of the invention to provide a scraper apparatus that will
more
precisely position the scraper element to better Gear debris from the
underbowl.
It is another object of the invention is to provide apparatus that can be
repaired without
replacing an entire assembly. In other words, it is an object of the invention
to provide
a consbuction that can be repaired faster, with less labor and at less e~ense
because
in and not necessary to replace the entire assembly to complete the repair.
It is another object of the invention to provide apparatus whiG~ may be
retrofitted easily
on e~dssting pulverizer apparatus.
Still another object of the invention is to provide apparatus which includes
discxete
portions that are most vulnerable to wear during the operating life and which
are
constructed so as to be readily replaced.
Yet another object of the invention is to provide a construction in which the
bearing
surface for the scraper element is spaced further away from the hostile
environment
than in the prior art construction.
One more object of the invention is to reduce the weight of the elements that
must
periodically be replaced so that the replacement will be easier.
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It has now been found that these and other objects of the invention may be
attained
in a scraper assembly for use with an associated coal puiverizer having a
vertical axis
with a central hub that rotates during normal operation of the pulverizer
which includes
a bracket dimensioned and configured for attachment to the hub of the
associated coal
pulverizer that rotates in the normal operation of the associated coal
pulverizer. The
apparatus also includes a shaft extending from the bracket. The shaft is
substantially
horizontal and the apparatus also indudes a scraping element pivotally mounted
on the
shaft; and means for biasing the scraping element with respect to the shaft.
In some forms of the invention the scraping element comprises a first and
second
journals engaging the shaft at axially spaced points and the scraping element
further
indudes first and second arms extending radially away from the shaft that are
respectively fixed to the first and second journals. The apparatus may further
indude
a first plate shaped member carried on the first and second arms and a second
plate
shaped member removabiy attached to the first plate shaped member.
The means for biasing may indude a spring which may be a torsion spring. Some
forms of the apparatus will indude means securing a first axial extremity of
the torsion
spring to the shaft and means securing a second axial extremity of the torsion
spring
to the first journal. The torsion spring may have a cylindrical shape that is
coaxial with
the shaft.
The invention also indudes a coal pulverizer apparatus which includes means
for
pulverizing coal induding a housing having a top and having an outlet at the
top for
discharge of pulverized coal and air. The means includes a bowl and a
plurality of rolls
and means for causing relative motion between the bowl and the plurality of
rolls and
a hub. A portion of the housing receives materials separated from pure coal
and the
apparatus includes a scraper assembly which includes a bracket dimensioned and
configured for attachment to the hub, a shaft extending from the bracket that
is
substantially horizontal and a scraping element pivotally mounted on the
shaft; and
means for biasing the scraping element with respect to the shaft.
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In some forms of the invention the scraping element comprise first and second
journals
engaging the shaft at axially spaced points, the scraping element further
includes first
and second arms extending radially away from the shaft, the first and second
all arms
are respectively fixed to the first and second journals and the apparatus
further
includes a first plate shaped member carried on the first and second arms.
In some forms of the invention the apparatus further includes a second plate
shaped
member removably attached to the first plate shaped member and the means for
biasing includes a spring which may be a torsion spring. The apparatus may
also
1o inGude means securing a first axial extremity of the torsion spring to the
shaft and
means securing a second axial extremity of the torsion spring to the first
journal. The
torsion spring may have a cylindrical shape and the spring may be coaxial with
the
shaft.
BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will be better understood by reference to the accompanying
drawing in
which:
Figure 1 is an elevational view, partially broken away and partially in
section of a
pulverizer incorporating the scraper assembly in accordance with one fomn of
the
present invention.
Figure 2 is a fragmentary, elevational, more detailed view of the scraper
assembly
illustrated in Figure 1.
Figure 3 is a plan view of the apparatus shown in Figure 2.
Figure 4 is a fragmentary sectional view taken along the line 4-4 of Figure 2.
Figure 5 is a fragmentary sectional view taken along the line 5-5 of Figure 2.
Figure 6 is a perspective view of the scraper assembly illustrated in Figure
1.
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DESCRIPTION OF THE PREFERRED EMBODIMENT:
Referting now to Figure 1, there is shown a putverizer 10 having an inlet 12
through
which the coal to be pulverized is fed. The coal falls into a bowl 14 that is
fixed to a
vertical shaft 16. A worm gear 18 is fixed to the shaft 16. A worm 20 is
driven by a
motor (not shown). Accordingly, the motor drives the worm 20 to drive the worm
gear
18 to tum the shaft 16 and thus tum the bowl 14. (Although the description
herein
refers to a worm gear, it will be understood by those skilled in the art that
other gear
systems may be used without departing from the present invention.)
The upper face of the bowl 14 is generally dish shaped. More particularly, the
upper
face includes a surface 14a that is dimensioned and configured for cooperation
with
a grinding roll 22. The grinding rol122 has a tn,rncated conical form.
The grinding roll 22 is mounted for rotation on a shaft 24 that is cartied on
a journal
t 5 assembly 26. The journal assembly 26 is mounted for pivotal motion about
an aide 28.
An adjustable stop 30 cooperates with a finger of the journal assembly 26.
More
particularly, the stop 30 allows adjustment to provide clearance between the
grinding
roll 22 and the face 14a.
The journal assembly 26 is biased by a spring assembly 32 so that it rotates
about the
axle 28 and abuts the stock 30. Those skilled in the art will recognize that
ordinarily
some clearance is desired intermediate the grinding roll 42 and the face 14a.
In operation, hot air is fed into the pulverizer 10 beneath the bowl 14. That
air is
directed past the vanes 36 in the region around the bowl 14. The hot air flows
past the
vanes 36 into the grinding area above the bowl 14. The hot air flows upwardly
around
the truncated cone shaped dassifier assembly 40. The classifier assembly 40
indudes
a plurality of openings 42 at the upper part thereof. Finely ground coal is
cartied by the
hot air from the area above the bowl 14 through the openings 42 and out the
exits 44,
44. Particles that are not as finely ground wilt fall, due to the effects of
gravity, back
down through the classifier assembly 40 and onto the face 14a of the bowl 14
where
they will be ground further until the particles are more finely ground.
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Although only one such grinding roll 22, shaft 24, and journal assembly 26 is
shown in
Figure 1, it will be understood by those skilled in the art that ordinarily
each puiveazer
of this general type will have three identical grinding rolls 22. Each of the
grinding
rolls 22 is carried on a shaft 24 that is carried in a journal assembly 26.
Each of the
5 three journal assemblies 26 is pivoted on an axle 28 and each is biased into
position
by a spring assembly 32. (Although the description herein refers to a spring
bias, it will
be understood by those skilled in the art that a hydraulic bias may be used
without
departing from the present invention.)
10 Pyrites and tramp iron mixed in with the coal initially are heavier than
pure coal and will
pass over the rim of the bowl 14 and onto the upper face 50 of the underbowl.
The
scraper assembly 52 in accordance with a preferred form of the present
invention is
provided to dislodge pyrites and tramp iron that accumulate on the face 50 of
the
underbowl and then through an exit chute (not shown).
As best seen in Figures 2-6, the scraper assembly 52 is disposed intermediate
the mill
hub 61 and the mill side 63. (Although only one scraper assembly 52 is shown
in the
drawing it will be understood that a typical mill will have two such scraper
assemblies.)
The scraper assembly 52 includes a base plate 54 to which is taxed a
horizontal shaft
56. The base plate 54 is mounted on a mounting plate 56 which is in turn
mounted on
a first generally triangular plate 58 and a second mounting plate 60 secured
to the hub
61 of the pulverizer 10. It will the understood that the hub 61 rotates during
normal
operation of the mill 10.
Cooperating with the horizontal shaft 56 are first and second journals 62, 64.
The first
and second journals 62, 64 are dimensioned and configured to allow free
rotation
about the horizontal shaft 56. Fixed respectively to the journals 62, 64 are
elongated
arms 66, 68. The elongated arms 66, 68 are each fixed to a plate 70 that
extends
radially across the upper face 50 all of the underbowl. Those skilled in the
art will
recognize that the arms 66, 68 and the plate 70 may be fabricated from a
single piece
of metal even though for description purposes they are described as discrete
elements
which are joined together. Mounted on the plate 70 is a replaceable wiper 72.
It will
be understood that the wiper 72 contacts the surtace 50 of the underbowl and
thus is
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subject to considerably more wear than other structural parts of the scraper
assembly
52. The wiper 72 is secured to the plate 70 by means of bolts 74,74,74. Thus,
the
wiper 72 may be easily replaced as wear occurs as part of the normal operation
of the
apparatus.
The wiper 72 is biased into the vertical position shown in the drawing by a
torsion
spring 76. The torsion spring 76 has one end thereof secured to the shaft 56
by a
stepped plate 78 secured to the shaft 56 by two set screws 80, 80. The
opposite axial
extremity of the torsion spring 76 is secured to the journal 62 by a planar
plate 82 that
is welded to both the torsion spring 76 and the journal 62. The torsion spring
76 allows
movement of the plate 70 and the wiper 72 if a large object contacts the wiper
72.
The apparatus in accordance with the invention also includes stop members 90,
92 that
limit the total travel of the assembly that includes the first and second
journals 62, 64;
etongated arms 66, 68; plate 70 and replaceable wiper 72. More particularly,
the stop
members limit total travel to 90 degrees. The stop 90 (best seen in Figure 2)
limits
movement past a vertical ptane. The stop 92 (best seen in Figures 2 and 3)
limits
movement past a horizontal plane.
It will thus be seen that the apparatus in accordance with the present
invention offers
enhanced operation and service life, is easier to install and maintain and can
be
installed as a replacement with little or no rework of existing parts. The
apparatus in
accordance with the invention over avoids the use of a vertically mounted
bushing that
tends to wear and and allow the scraper to droop and touch directly on the
pulverfzer
floor liner and cause excessive wear. The structure in accordance with the
present
invention moves the pivot away from the floor area to a horizontal position
spaced
away from the bottom of the mill.
This provides better support for the assembly and allows the scraper to do a
better job
clearing debris from the mill bottom. The torsion spring 76 provides enough
resistance
to remove debris from the mill bottom while still allowing the arm to fold
back over
larger, immovable objects so that neither the assembly nor the rest of the
mill is
damaged by such materials.
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In addition, wom or broken complements will ordinarily require replacement.
For
example, the replaceable wiper or wear ptate 72 mounted on the plate 70 can be
replaced without the need for other elements being replaced. The use of
smaller and
lighter replaceable elements is also advantageous. The smaller and lighter
elements
are easier to handle and can be quickly replaced on an as needed basis. Thus,
the
scraper assembly 52 is easier to maintain.
The invention has been described with respect to its preferred embodiment.
Persons
skilled in the art of such devices may upon exposure to the teachings herein
conceive
other variations such the relations are deemed to be encompassed by the
disclosure,
the invention being delimited only by the following claims.
We claim:
